Numerous patents illustrate Tee-nut insertion machines. Such Tee-nuts-are widely used for example in the furniture industry. They consist of a threaded sleeve, and a relatively wide flange or head, all being made integrally out of sheet metal. Teeth or prongs extend from the flange or head. Such nuts are inserted into wooden items of the furniture. They serve as a point of attachment for securing a threaded fastener.
Almost all such machines are operated by compressed air, powering a power cylinder which is connected to an insertion plunger. Almost all such machines employ some form of magazine or Tee-nut supply system for supplying Tee-nuts to the plunger. Such machines are usually operated by an operator, who must stand at the machine and hold the wooden workpiece in position in registration with the Tee-nut. He must locate the precise point for insertion of the Tee-nut in registration with the Tee-nut and then activate the machine. This is usually done by means of a foot pedal. Obviously wide variations are possible on this system, but this system described is the system in widest use. Most such machines operate on a downward insertion cycle. In this system the Tee-nut and plunger are located above the wooden workpiece. The wooden workpiece rests on a wooden rest. Upon activation, the plunger descends downwardly, and picks up a Tee-nut, and forces it into the workpiece.
There are, however, variations on this in which an upward insertion system is used. In this system the plunger and Tee-nut are located below the wooden workpiece, and the rest or stop is located above the plunger.
Generally speaking, such systems employ air cylinders, in which the piston is forced downwardly (or upwardly in some cases) at a high velocity, so as to provide sufficient force to drive the Tee-nut into the workpiece. Usually the Tee-nut is being driven into a pre-drilled hole, but in some cases the Tee-nut is simply driven directly into the workpiece and the plunger punches a hole in the workpiece, as the same time as the nut is inserted. An example of this system of self punching Tee-nut is shown in U.S. Letters Patent 5,323,531 dated Jun. 28, 1994 Title: Self Punching Tee-Nut Insertion Machine, Inventor: Walter H. Leistner et al.
It has now been found that the high velocity air cylinder form of driving mechanism has certain disadvantages.
In the first place, the relatively high speed of the piston and plunger set up severe shock and vibrations in the workpiece which can damage the workpiece.
Secondly, such systems result in relatively high consumption of compressed air for each stroke. While this may not be a significant factor in some cases, it does mean that in a large factory very substantial compressed air supplies must .be provided, in order to ensure sufficient compressed air for the operation of multiple machines.
A third factor is that the depth of insertion of Tee-nuts into a workpiece may vary due to the hardness of the workpiece. Since the workpiece may be made of processed wooden materials or synthetic non-wooden materials of variable densities, different workpieces may be of different hardness. The plunger of a high velocity Tee-nut insertion machine may cause Tee-nuts to be inserted undesirably deeper into the surfaces of the workpiece of lower density and damage its structure.